Hybrid ship propulsion system

ABSTRACT

A hybrid propulsion system includes a main diesel engine for driving the marine turbine and an electric motor. The electric motor has a nominal output that constitutes at least 20% of the nominal output of the main diesel engine. The electric motor remains continuously switched on and maintains, together with a variable-pitch propeller, the main diesel engine at a favorable operating point. The combination of the main diesel engine and the electric motor also allows for a more economical design or operation of the propulsion system.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/DE01/04556 which has an Internationalfiling date of Dec. 5, 2001, which designated the United States ofAmerica and which claims priority on German Patent Application numbersDE 100 61 578.3 filed Dec. 11, 2000, the entire contents of which ishereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

The propulsion system for large cargo ships, for example containerships, normally provides one slow-running diesel engine for each shippropeller. This slow-running diesel engine supplies all the propulsionpower for this propeller. The propulsion power of the diesel enginestarts at about 10 to 15 MW. The diesel engines that are used operate onthe two-stroke principle. The high power that is required and the lowrated rotation speed result in a large swept volume, and thus a largephysical volume with a large mass.

A correspondingly large amount of space must be provided in the ship'shull for the diesel engine or, for a multishaft propulsion system, thediesel engines, to be precise at a point which is located close to thestern with respect to the overall length. The engine room is located ata point which intrinsically would be particularly highly suitable forbeing loaded with containers. There is also a large amount of unuseddead space.

Because of the heavy weight of the diesel engine, the hull must bereinforced to a considerable extent at the relevant points.

Besides the diesel drive for ships, it is also known from practice forelectric motors to be used for driving the ship propeller. Theelectrical power for the propeller motor is produced by means of adiesel generator system. High-speed four-stroke diesel engines can beused in this case, which have a considerably better power-to-weightratio than slow-running diesel engines. Their rotation speed is higherby a factor of approximately 4 to 10 than the rotation speed of thediesel engine for the ship propeller.

Furthermore, converters based on semiconductors can be used to alwaysoperate the diesel engine for the diesel generator system independentlyof the load at that rotation speed at which the fuel consumption withrespect to the output power is optimum. This propulsion system conceptmakes it possible to avoid thermal problems resulting from low rotationspeeds and high cylinder charges.

The considerable advantages of an electrical propulsion system arecountered by comparatively high investment costs, which are considerablygreater than the costs involved for a diesel engine that drives the shippropeller directly.

Finally, a mixed propulsion system is known from practice, whichprovides a slow-running diesel engine for the ship propeller as the mainpropulsion device. In addition, a comparatively small electric motor iscoupled to the propeller shaft, as a booster. The electric motor poweris at most 10% of that of the diesel engine.

The booster motor is used in particular in the low rotation speed rangein order to avoid thermally overloading the main propulsion systemdiesel. A further purpose of the booster motor is to improve the controlsystem dynamic response, for example in operating situations when thepropeller is partially moving in and out of the water owing to heavy seastates.

SUMMARY OF THE INVENTION

Against this background, an object of an embodiment of the invention isto provide a ship propulsion system which is more economic overall thanthe known systems. Preferably, this is from the viewpoint of fuelconsumption in operation, of the available useful area, and/or theinvestment costs for the ship's hull and the propulsion system duringconstruction of the ship.

According to an embodiment of the invention, this object is achieved bya ship propulsion system.

The ship propulsion system according to an embodiment of the inventionuses a combination of an electrical drive and a diesel drive for theship propeller. The electric motor is relatively large and provides asignificant proportion of the total propeller torque with respect to thetorque which is supplied by the diesel engine. Nonetheless, whenconsidered overall, the electrical power of the electric motor is stillrelatively small, so that the investment costs can be kept low, comparedto a propulsion system operating entirely with electric motors.

The electric motor replaces, so to speak, one or more cylinders of theslow-running diesel engine, which becomes correspondingly shorter andlighter, compared to a ship in which this propulsion power originatesexclusively from a slow-running diesel engine. The reduction in volumeand mass for the main diesel is greater than the weight and spacerequired for the electric motor and its power supply. Both the electricmotor and its power supply can be accommodated in the dead space whichwould otherwise exist within the engine room.

The reduction in the space required for the main diesel engine, comparedto a propulsion system in which the propulsion power is provided mainlyby the slow-running diesel engine, considerably increases the cargocapacity without changing the ship dimensions.

Furthermore, the diesel generator system can be accommodated virtuallyanywhere in the ship's hull, that is to say even at points which are notparticularly well suited in any case for accommodating containers orother cargo.

The mixed propulsion system with the relatively high electricalpropulsion power, in conjunction with the variable-pitch propeller, nowalso makes it possible to achieve an advantageous regulated fuelconsumption by the main diesel engine in virtually all operatingsituations.

In particular, it is possible to overcome the thermal load on the maindiesel engine during starting and acceleration of the ship, thusconsiderably improving the life and reducing the amount of maintenancework for the main diesel engine.

The new propulsion system concept is also suitable for conversion orupgrading of existing ships, without needing to enlarge the engine room.

By way of example, this propulsion system concept allows a seagoing shipto be converted to a ship which can pass through ice, or even to anice-breaking cargo ship. All that is necessary for this purpose is toreinforce the hull in the appropriate areas of the bow and of the bottomof the ship, as well as the flanks, for ice operation.

Virtually no changes are required to the main diesel for the propellershaft or shafts. In particular, the power is increased without enlargingthe engine room.

The shaft system is upgraded as appropriate for the greater totalpropulsion power, and the additional electrical propulsion system isinstalled. The space required for the additional electric motor and forthe diesel generator system is small with respect to the dead spaceavailable in the engine room. The additional devices can generally beaccommodated without any problems.

The new propulsion concept also makes it possible to give an existingcontainer ship or cargo ship a higher cruise speed. For this purpose, asmentioned above, the shaft system is reinforced, possibly with avariable-pitch propeller being fitted, and the propeller shaft beingprovided with the electric motor. In this case as well, the dieselgenerator system can be accommodated in the engine room or at some otherpoint, once again without any difficulties.

A ship that has been converted in this way is able to achieve highercruise speeds when moving freely, without any changes to the externaldimensions.

It is also possible to use the new propulsion system concept to enlargethe cargo volume rather than to increase the cruise speed when movingfreely of a cargo ship, if this is what is required. This is done bylengthening the ship's hull to correspond to the desired volume. Themain diesel is retained, and is assisted in the manner according to theinvention by an electrical propulsion system. There is no need toenlarge the engine room in this case either, that is to say the maindiesel remains in the same place. It is sufficient to match the shaftsystem to the increased torque, to provide a variable-pitch propellerand to install the diesel generator system.

As is evident, upgrading can be carried out in one of the directionsmentioned above at any time comparatively easily, without any majorchanges being required in the area of the engine room or of the maindiesel engine or engines.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the invention will becomeevident from the description of illustrated exemplary embodiments givenhereinbelow and the accompanying drawings, which are given by way ofillustration only and thus are not limitative of the present invention,wherein:

FIG. 1 shows a ship which is equipped with the hybrid propulsion systemaccording to an embodiment of the invention, in the form of a highlyschematic longitudinal section, and

FIG. 2 shows the outline circuit diagram of the hybrid propulsion systemaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a highly schematic illustration of a container ship 1 witha ship's hull 2 and a superstructure 3. The ship's hull 2 is cut away inthe area of an engine room 4. The illustration is not to scale at all,with the only aim being to show the essential items.

The engine room 4 has an engine room deck 5 and is closed in the forwarddirection, in the direction of the ship's bow, by a bulkhead 6. It isclosed in the rearward direction by the corresponding stern part of theship 1. A ship propeller 7 is arranged in a known manner in an area ofthe stern that is shown, and is connected to a propeller shaft 8 suchthat they rotate together. The ship propeller 7 is what is referred toas a variable-pitch propeller, that is to say a propeller with propellerblades 9 whose pitch can be varied. A rudder 11 is fitted downstreamfrom the propeller 9, such that it can swivel.

The propeller shaft 8 passes through a propeller shaft pipe 12, which issupported by at least one support 13 in the interior of the ship. Thepropeller shaft pipe 12 is followed by a radial bearing 14, which islikewise mounted on the engine room deck 5 and is used to absorb some ofthe radial force of the ship's shaft 8. As it continues, seen in thedirection of the bow of the ship 1, there is an electric motor 15, whoserotor shaft is formed by the propeller shaft 8.

The electric motor 15 may be a synchronous machine, an asynchronousmachine or a DC machine. In any case, it is a slow-running motor, whichpreferably acts directly on the propeller shaft 8, without anyintermediate gearbox.

Finally, the propeller shaft 8 is also supported by a further bearing16, which is likewise mounted on the engine room deck 5 and absorbs theaxial forces and radial forces, that is to say the thrust produced bythe propeller 7.

Finally, at the end, the propeller shaft 8 is connected to aslow-running main diesel engine 17, whose crankshaft drives thepropeller shaft 8 either directly or via single-stage step-down gearing.The main diesel engine 17 is a two-stroke diesel engine and typicallyhas a rated power of at least between 8 and 13 MW. The present-day powerrange for single engines extends up to about 70 MW for cargo ships.

A schematically indicated control drive 18 is provided for controllingthe ship propeller 7.

The power supply for the electric motor 15 is provided by a dieselgenerator set 19 which, in the illustrated exemplary embodiment, isarranged on a gallery deck 20 in the engine room 4. This dieselgenerator set 19 has a diesel engine 20 as well as an electricitygenerator 22. The diesel engine 21 is a high-speed diesel engine whichoperates on the four-stroke principle.

Two or more diesel generator sets may also be used instead of a singlediesel generator set 18, and are connected in order to supplyelectricity depending on the power demand.

The electric motor 15 and the main diesel engine 17 form a hybridpropulsion system for the ship propeller 7. The rated power of theelectric motor 15 represents at least 20 percent of the rated power thatthe main diesel engine 17 can emit. Thus, when the maximum torque isapplied to the ship propeller 7, approximately 20 percent of the torqueis provided by the electric motor 15, while the rest is produced by themain diesel engine 17.

The illustration in FIG. 1 is not to scale to the extent that the volumeof the main diesel engine 17 is very much greater than the volume of thediesel engine 21 for the diesel generator set 18, but it would bevirtually impossible to show this in comparison to the main dieselengine 17.

The electric motor 15 is operated during every operating phase of theship propulsion system and is controlled overall such that the maindiesel engine 17 is thermally loaded as little as possible and/or has asgood a fuel consumption as possible.

The electrical equipment for operating the hybrid propulsion system isshown in highly schematic form in FIG. 2.

The diesel set 18 feeds its electrical power to an electrical powersupply system 23. Electrical power for further electrical devices istapped off from the power supply system 23 via a switch 24. The powersupply system 23 is also connected via a switch 25 to a converter 26,which produces field energy for the electric motor 15 via a cable 27.The field energy for a synchronous machine is produced via a converter28, which is likewise connected to the power supply system 23 via aswitch 29. The electrical power for the electric motor 15 is measured atthe input of the converter 28, and is passed to a central controller 32,by means of a control line 31.

The central controller 32 uses a control line 33 to control theconverter 28, and a control line 34 to control the converter 26. Via aline 35, the central controller 32 also detects the rotation speed ofthe electric motor 15, that is to say of the propeller shaft 8.

The central controller 32 is also connected via lines 36 to the commandbridge, an alarm system, a remote maintenance device and other suchdevices. The central controller 32 also determines the fuel consumptionof both the main diesel engine 17 and of the diesel set 18 and controlsthe entire system so that the overall fuel consumption is optimized.Finally, the central controller 32 also provides the control functionfor the control drive 18.

The hybrid propulsion system according to the invention occupies a verysmall amount of space in comparison to the main diesel engine 17. It istherefore possible to upgrade existing seagoing ships with the hybridpropulsion system according to an embodiment of the invention. Thisupgrading is carried out without the engine room occupying any largeramount of space. The additional facilities, such as the electric motor15 and the diesel set 18, can be accommodated without any problems inthe dead space in the engine room which is not used by the main dieselengine 17.

By way of example, it is thus possible to convert an existing seagoingship to a ship which is capable of passing through ice, or even into anicebreaker. The propulsion power is stepped up for this purpose byadditionally coupling an electric motor to the respective propellershaft. If this has not already been done, the ship propeller isconverted to a variable-pitch propeller, and the additionally requireddiesel generator set is installed. The propeller shaft pipe and theshaft bearings may possibly need to be reinforced, to match theincreased propulsion power.

The bow, the bottom of the ship in the bow area and the flanks of theship must, of course, also be reinforced for a ship which is capable ofpassing through ice or for an icebreaker.

The hybrid propulsion system concept according to an embodiment of theinvention also makes it possible to increase the propulsion powerretrospectively for an existing ship. This can be done in order toachieve higher cruise speeds. This is done by converting the propulsionsystem of the ship in the same way as that already explained above.

Finally, it is feasible to use the hybrid propulsion system according toan embodiment of the invention to increase the propulsion power to suchan extent that it is possible to enlarge or lengthen the ship's hull inorder to increase the cargo area, with the same cruise speed.

The propulsion system concept according to an embodiment of theinvention can be used not just for single-shaft systems but also formultishaft systems. Furthermore, it is also feasible for the electricmotor to be coupled to the propeller shaft via a gearbox rather thanbeing arranged directly on the propeller shaft. Finally, it is feasiblefor the electric motor to be coupled to the crankshaft of the maindiesel engine, to be precise on the opposite side from the propellershaft.

If single-stage gearing is connected between the electric motor and thepropeller shaft, it may be possible to use an even smaller electricalmachine in some circumstances. A hybrid propulsion system includes amain diesel engine for driving the ship's shaft, and an electric motor.The electric motor has a rated power which corresponds to at least 20%of the rated power of the main diesel engine. The electric motor isswitched on all the time and, in conjunction with a variable-pitchpropeller, ensures that the main diesel engine is kept at anadvantageous optimum operating point. The combination of the main dieselengine and the electrical drive thus, overall, allows more economicconstruction and operation.

Exemplary embodiments being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the present invention, andall such modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

1. A ship propulsion system for seagoing ships (1) having at least oneship propeller (7) which is driven via a propeller shaft (8) and hasvariable-pitch propeller blades (9), having a control drive (18) forcontrolling the propeller blades (9), having a slow-running main dieselengine (17), which has a predetermined rated power and is coupled to thepropeller shaft (8) in order to supply power to the ship propeller (7),having an electric motor (15) which has a predetermined rated power andis coupled to the propeller shaft (8) in order to supply power to theship propeller (9), with the rated power of the electric motor (15)being at least twenty percent of the rated power of the main dieselengine (17), having an electricity generator system (21) for producingelectrical power for the electric motor (15), and having a fast-runningdiesel system (20) for driving the electricity generator system (21). 2.The ship propulsion system as claimed in claim 1, characterized in thata control device (32) is provided in order to control the torque whichis emitted from the electric motor (15) such that the slow-running maindiesel engine (17) is operated as close as possible to a predeterminedoperating point.
 3. The ship propulsion system as claimed in claim 1,characterized in that a control device (32) is provided for controllingthe ship propeller (7) such that the slow-running main diesel engine(17) is operated as close as possible to a predetermined operatingpoint.
 4. The ship propulsion system as claimed in claim 1,characterized in that the optimum operating point is the operating pointwhich produces the least thermal load on the slow-running main dieselengine (17).
 5. The ship propulsion system as claimed in claim 1,characterized in that the optimum operating point is the operating pointat which the slow-running main diesel engine (17) has the lowest fuelconsumption.
 6. The ship propulsion system as claimed in claim 1,characterized in that the electric motor (15) is a synchronous machine,an asynchronous machine or a DC machine.
 7. The ship propulsion systemas claimed in claim 1, characterized in that the electric motor (15) istorque-controlled.
 8. A method for operating a seagoing ship which isequipped with one or more ship propulsion systems as claimed in one ormore of the preceding claims, in that, at a given ship speed without anyacceleration, the electric motor (15) and the ship propeller (7) arecontrolled such that the total fuel requirement for the slow-runningmain diesel engine and for the diesel generator system (19) isminimized.
 9. A method for upgrading the propulsion power of an existingseagoing ship (1) by means of at least one electric motor (15), whichhas at least one shaft system (7, 8, 12, 14) with a propeller shaft (8)for driving a ship propeller (7) and has at least one slow-running maindiesel engine (17) for driving the propeller shaft (8), having thefollowing steps:
 10. - an electric motor (15) is provided, whose ratedpower is at least 20% of the rated power of the slow-running main dieselengine (17) which is intended to be supplemented by the electric motor(15), - a diesel generator system (19) is installed, - the shaft system(7, 8, 12, 14) is matched to the total power of the electric motor (15)and of the slow-running main diesel engine (17), and - an electricalcontrol and regulation device (32) is installed, in order to control thetorque which is to be emitted from the electric motor (15) to thepropeller shaft (8).
 11. A method for upgrading a seagoing ship,characterized in that the ship's hull (2) is reinforced in order to makethe seagoing ship capable of passing through ice.
 12. A method forupgrading a seagoing ship, characterized in that the ship propeller (7)is replaced by a ship propeller (7) whose propeller blades (9) arecontrollable, and in that a control drive (18) is installed for thepropeller blades (9).